20 HP Kohler Command engine rebuild

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murraym

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I am rebuilding a CH20S-64549 Kohler Command 20 HP engine for my lawn mower. I would like to replace the valve guides, however, it is proving difficult to find just the valve guides. I've tried some of the larger internet sites and spoke to Kohler. Everyone says I need to replace the heads with new ones if I want new guides. Does anyone know of a good source for parts other than Jacks, ereplacmemnts, parts tree etc. I might even be open to attempting to make some if I had an idea of what type of bronze to use or if it matters, and the amount of clearance needed for the valve itself. Has anyone ever done this before? any tips of things to look for? These things can sometimes sound easy in theory.....

Thank you all in advance,

Mike
 
I've replaced guides in many Briggs racing motors and would generally agree that if yours are worn out a replacement head probably offers a better value. Once you change the guides you will at a minimum have to re-cut the valve seats and lap the valves in. I have the tools to do this but they aren't cheap and learning how to do it for one engine would be potentially an exercise in futility.

I'm not sure what your experience with small engines is, how much the heads cost, or how sloppy your guides are. If you have a new valve you can see if the wear is on the valve itself or in the guide since measuring the bore isn't easy with hobby machine measuring tools. If you really want to replace the guides perhaps you can get a suitable replacement from Briggs provided you can figure out the measurements.

But, replacing the heads will give a much better chance of having your rebuild last.

Knowing what goes into a quality rebuild I would be tempted to opt for a re-power if the mower was a really good one (like a zero turn or big hydrostatic). Harbor Freight offers one pretty cheap.

www.harborfreight.com

22 HP (670cc) V-Twin Horizontal Shaft Gas Engine, EPA

Amazing deals on this 22Hp (670Cc) V-Twin Horiz Shaft Gas Engine at Harbor Freight. Quality tools & low prices.
www.harborfreight.com www.harborfreight.com

or sometimes you can buy surplus from someone like this.

Buy replacement gasoline engines for lawnmowers and equipment from Small Engine Warehouse

www.smallenginewarehouse.com www.smallenginewarehouse.com

I'm sure you could make valve guides that would fit your heads but getting them installed and having them last might be a challenge. FWIW I did a ton of re-powers in the shop I ran for 5 years, I would only rebuild something if I couldn't get a new motor and the tool was really worth it. Something I rarely saw with modern equipment.


John
 
matthewsx said:
I've replaced guides in many Briggs racing motors and would generally agree that if yours are worn out a replacement head probably offers a better value. Once you change the guides you will at a minimum have to re-cut the valve seats and lap the valves in. I have the tools to do this but they aren't cheap and learning how to do it for one engine would be potentially an exercise in futility.

I'm not sure what your experience with small engines is, how much the heads cost, or how sloppy your guides are. If you have a new valve you can see if the wear is on the valve itself or in the guide since measuring the bore isn't easy with hobby machine measuring tools. If you really want to replace the guides perhaps you can get a suitable replacement from Briggs provided you can figure out the measurements.

But, replacing the heads will give a much better chance of having your rebuild last.

Knowing what goes into a quality rebuild I would be tempted to opt for a re-power if the mower was a really good one (like a zero turn or big hydrostatic). Harbor Freight offers one pretty cheap.

www.harborfreight.com

22 HP (670cc) V-Twin Horizontal Shaft Gas Engine, EPA

Amazing deals on this 22Hp (670Cc) V-Twin Horiz Shaft Gas Engine at Harbor Freight. Quality tools & low prices.
www.harborfreight.com www.harborfreight.com

or sometimes you can buy surplus from someone like this.

Buy replacement gasoline engines for lawnmowers and equipment from Small Engine Warehouse

www.smallenginewarehouse.com www.smallenginewarehouse.com

I'm sure you could make valve guides that would fit your heads but getting them installed and having them last might be a challenge. FWIW I did a ton of re-powers in the shop I ran for 5 years, I would only rebuild something if I couldn't get a new motor and the tool was really worth it. Something I rarely saw with modern equipment.


John
Click to expand...

Thank you for your reply.

My experience with small engines is that I typically change the oil regularly and they will outlast the equipment they are attached to. The reason I am really interested in fixing this one is that it is a full frame garden tractor built by Troy Bilt before MTD got ahold of them. I also use it for more than just mowing. there is a 40 inch rototiller, 48 inch snowblower with a cab, leaf collector unit which works great for my 2 acres of leaves in the fall, and I have attached a spray rig for spraying the yard for weeds, fruit trees etc.

The valve seats do need some attention but do not look all that bad. I could attach pics if you would like to see. New heads would be about 350. I would look at a re power, however I am not familiar enough to know about how a new engine would fit. Are small engines like electric motors with frame sizes? For example, if I were to buy a new engine, would things like the electric clutch mounting be on the front cover and line up with the drive pulley? I just don't know.

I do want this rebuild to last. the tractor is roughly 25 years old but in great shape. If new heads is the way to go, the total rebuild would be about 850. I suppose that's not bad if I can get another 20 years......I don't even know if that's possible.

Mike
 
I've done a lot of Mag 20s and 18s in the Cub SGTs . I never got into the newer stuff so this may be an interesting thread . I'm following along .
 
You may want to alert Fin . He's a Cub rebuilder also . We're both over on the Only Cub Cadet site . :encourage:
 
What’s the reason for new valve guides? To get kohler parts I would go to a authorized dealer and order the parts. I rebuild all types of engines from little 2-strokes to 30hp diesel Kubotas. You should be able to google your model and find results. I always have the model, spec, and family numbers which are on the engine tag. Which spec tells crank diameter a Length and other variable of engine.
As to replacing valve guides it can be done but the possibility of the head crumbling at the joint of the two materials is likely. Fixturing the head to get good alignment, heating the head for the install. Then reaming and cutting lapping valves. And all can go to waste on pressing the second guide and the valve seat pops out from the pressure.
I’d either buy new valves and lap them install new valve seals maybe even springs but to do the guides your better off with a complete new head. what kind of hours we talking on the tractor?
 
Both Cub and Troy Bilt were great before the consolidation and buy out times.

I’ve had good luck with Small Engine Warehouse in the past. They usually have specs and drawings available for engines they sell so you can compare with the measurements from yours. HF has the info in their documentation here.


If a rebuild will cost $850 and a repower is $800 I think you have your answer.

Lots of guys will spend big bucks on their classics but if it’s about getting work done any power plant will make that happen.

First step is to pull it off, then decided from there what path to take.

John
 
And yes, pictures.

Always pictures ;)
 
Cadillac said:
What’s the reason for new valve guides? To get kohler parts I would go to a authorized dealer and order the parts. I rebuild all types of engines from little 2-strokes to 30hp diesel Kubotas. You should be able to google your model and find results. I always have the model, spec, and family numbers which are on the engine tag. Which spec tells crank diameter a Length and other variable of engine.
As to replacing valve guides it can be done but the possibility of the head crumbling at the joint of the two materials is likely. Fixturing the head to get good alignment, heating the head for the install. Then reaming and cutting lapping valves. And all can go to waste on pressing the second guide and the valve seat pops out from the pressure.
I’d either buy new valves and lap them install new valve seals maybe even springs but to do the guides your better off with a complete new head. what kind of hours we talking on the tractor?
Click to expand...

The reason for new guides is that there is some slop in the current ones. I'm not sure how to quantify exactly how much slop but if the valve is open enough to grab it with your fingertips, you can wiggle the valve enough to feel it and see it. In fact, I think you can see the oblonged hole in the guides when looking at the ends. There was about 1300 hrs on the engine. IDK if that is a lot or not. Maybe I am making a bigger deal of this than it is. I would think that they should be tighter. The engine was running fine until it quit.
Pics to follow.......

Thank you.
Mike
 
matthewsx said:
Both Cub and Troy Bilt were great before the consolidation and buy out times.

I’ve had good luck with Small Engine Warehouse in the past. They usually have specs and drawings available for engines they sell so you can compare with the measurements from yours. HF has the info in their documentation here.


If a rebuild will cost $850 and a repower is $800 I think you have your answer.

Lots of guys will spend big bucks on their classics but if it’s about getting work done any power plant will make that happen.

First step is to pull it off, then decided from there what path to take.

John
Click to expand...

I will check out Small Engine wharehouse. Thank you.
 
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